1. Field of the Invention
The present invention relates to a sheet conveying apparatus conveying sheets.
2. Description of the Related Art
A conventional electrophotographic type copying machine has a configuration in which, when a registration roller provided immediately upstream of a photosensitive drum is stopped, skewing of sheets is corrected by causing a fed sheet to hit a the nip of the registration rollers. In a copying machine having a long conveying path from the feeder to the photosensitive drum, following sheets are sequentially fed without waiting for image forming on the preceding sheet by the photosensitive drum, to improve productivity of the copying machine. As a result, there exist a plurality of sheets on the conveying path from the feeder to the photosensitive drum.
During the time skewing of the sheet is corrected, the sheet is substantially stopped in position at the registration rollers. To prevent the following sheet from catching up the preceding sheet, therefore, the following sheet is also temporarily stopped in dependence thereon. Then, the roller immediately upstream of the photosensitive drum and the rollers from the feeder to the photosensitive drum are simultaneously driven, and feeding of a plurality of sheets on the conveying path is resumed.
There is at present a demand for further improvement of productivity of the conventional copying machine as described above, and for this purpose, it is necessary to further reduce the sheet interval. However, a sheet interval shorter than the conventional one poses a problem of a shift of the sheet stopping position. A roller for feeding sheets is driven by a DC motor via a clutch, which is released when causing the sheet to temporarily stop. When the clutch is released, the roller stops as a result of the effect of friction of the bearing of the roller. Because the roller is stopped through bearing friction, the roller slightly rotates during the period from clutch release to roller stoppage, and the following sheet held by the roller approaches the preceding sheet that is in contact with the registration roller. Feeding of all the sheets in temporary stoppage on the conveying path is resumed at a time. The sheets are often fed therefore with a very short distance between the trailing edge of the preceding sheet and the leading end of the following sheet, thus resulting in an abnormality in conveyance control of the sheets. The stoppage characteristics of the roller might be different from the one of the other roller because of the individual difference. Also, the stoppage characteristics of the roller might be changed because of the secular change.
Accordingly, it is an object of the present invention to provide a sheet conveying apparatus solving the above-mentioned problems.
The present invention provides a sheet conveying apparatus comprising a sheet feeder which feeds sheets at predetermined sheet intervals; a conveyor which conveys a plurality of sheets fed by the sheet feeder; a controller which, after temporarily discontinuing conveyance of the plurality of sheets by the conveyor, resumes conveyance of the plurality of sheets by the conveyor; and a corrector which corrects, upon resuming sheet conveyance, variations in the sheet interval caused upon temporarily discontinuing sheet conveyance.
In the sheet conveying apparatus of the invention, the corrector delays the resumption of conveyance of a following sheet by a time corresponding to a decrease in the sheet interval which is caused upon temporary discontinuance of sheet conveyance.
The invention also provides a sheet conveying apparatus comprising a feeder which feeds first, second and third sheets at predetermined intervals; a conveyor which conveys the first, second and third sheets fed by the feeder to a registration roller; a controller which, after temporarily discontinuing conveyance of the first, second and third sheets by the conveyor in response to arrival of the first sheet at the registration roller, resumes conveyance of the first, second and third sheets by the conveyor; and a corrector which corrects a variation in the sheet interval between the first sheet and the second sheet upon resuming conveyance of the second sheet, and corrects a variation in the sheet interval between the second sheet and the third sheet upon resuming conveyance of the third sheet.
The aforementioned corrector, in the aforementioned sheet conveying apparatus, resumes conveyance of the second sheet by delaying by a first period of time corresponding to the sheet interval between the first and second sheets which is decreased upon temporary discontinuance of sheet conveyance, and resume conveyance of the third sheet by delaying by a second period of time corresponding to the sheet interval between the second and third sheets which is decreased upon temporary discontinuance of sheet conveyance.
In another respect, the invention provides a sheet conveying apparatus comprising a roller which conveys sheets; a driver which generates a driving force to drive the roller; a clutch which transmits a driving force of the driver to the roller; a controller which controls engagement and disengagement of the clutch; and a memory which stores data of stop characteristics of the roller upon disengagement of the clutch; wherein the controller controls a connecting timing of the clutch on the basis of the data stored in the memory.
The aforementioned controller delays the reengagement of the clutch by a period of time corresponding to the data stored in the memory.
The aforementioned controller controls engagement of the clutch after causing disengagement of the clutch; and when the time from causing disengagement of the clutch to causing engagement of the clutch is shorter than the period of time corresponding to the data stored in the memory, the controller delays the engagement of the clutch by a period of time.
The data of stop characteristics of the roller stored in the memory are data corresponding to an amount of lead of a sheet conveyed by the roller upon disengagement of the clutch.
In the above-mentioned sheet conveying apparatus, data corresponding to an amount of lead of the sheet conveyed by the roller upon disengagement of the clutch based on a time required for conveying a sheet from a first position to a second position without disengaging the clutch, and a time required for conveying a sheet from the first position to the second position when the clutch is reengaged after disengaging the clutch when the sheet is present between the first position and the second position.
The invention provides also a sheet conveying apparatus comprising first, second and third rollers which convey sheets; a driver which generates a driving force to drive the first, second and third rollers; first, second and third clutches which transmit a driving force of the drive to the first, second and third rollers; a controller which controls engagement and disengagement of the first, second and third clutches; and a memory which stores first data of stop characteristics of a sheet upon disengagement of the first and second clutches while the first and second rollers hold the sheet in between, and second data of stop characteristics of the sheet upon disengagement of the second and third clutches while the second and third rollers hold the sheet in between; wherein the controller controls the engagement timing of the first, second and third clutches on the basis of any of the first and second data stored in the memory.
The first and second data stored in the memory comprise data corresponding to an amount of lead of the sheet conveyed by the first and second rollers upon disengagement of the first and second clutches, and data corresponding to an amount of lead of the sheet conveyed by the second and third rollers upon disengagement of the second and third clutches.
The controller selects one of the first and second data, depending upon by which of the first, second and third rollers the sheet is held in between.
The aforementioned controller selects the first data when the sheet is held by the first and second rollers in between, not by the third roller in between, and selects the second data when the sheet is held by the second and third rollers in between, not by the first roller.
The aforementioned controller selects the first data if the sheet is held by the first, second and third rollers in between when the first data show stop characteristics for stoppage of the sheet within a shorter period of time than the second data.
The aforementioned controller selects the second data if the sheet is held by the first, second and third rollers in between when the second data show stop characteristics for stoppage of the sheet within a shorter period of time than the first data.
The present invention provides a sheet conveying apparatus comprising a conveyor which conveys sheets along a conveying path; a controller which, after temporarily discontinuing sheet conveyance during conveyance of the sheet by the conveyor, resumes sheet conveyance; a first sensor provided on the conveying path; a second sensor provided in the downstream of the first sensor on the conveying path; and a measurer which causes the conveyor to convey the sheet, causes sheet conveyance to stop when a sheet is between the first sensor and the second sensor; resumes sheet conveyance after the lapse of a predetermined period of time; and measures a first period of time from detection of an edge of the sheet by the first sensor to detection of an edge of the sheet by the second sensor.
The conveyor contains a first roller which conveys sheets; the first sensor is provided upstream of the first roller, and the second sensor is provided downstream of the first roller.
The aforementioned controller controls the timing for resuming conveyance in response to the result of measurement by the measurer.
The above-mentioned sheet conveying apparatus further comprises a third sensor provided downstream of the second sensor in the conveying path; wherein the measurer causes the sheet having temporarily stopped between the first sensor and the second sensor to stop between the second sensor and the third sensor; resumes sheet conveyance after the lapse of a predetermined period of time; and measures a second period of time from detection of an end of the sheet by the second sensor to detection of an end of the sheet by the third sensor.
The conveyor contains a first roller and a second roller; the first sensor is provided upstream of the first roller; the second sensor is provided between the first roller and the second roller; and the third sensor is provided downstream of the second roller.
The above-mentioned controller controls the timing for resuming conveyance in response to any of the first period of time and the second period of time.
The aforementioned sheet conveying apparatus further comprises a terminal for entering an instruction to start a measuring mode for measuring characteristics of the conveyor during stoppage of conveyance and upon resumption of conveyance by the conveyor; wherein measurement is started in response to input of the instruction to start the measuring mode from the terminal.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.